birth control

well I've been on birth control for a long time ( a year now ) and my periods are irregular, well I am a very tiny girl I'm 5'2 and weighed 106 pounds well since may I've still had irregular periods, all my test have come up negative, well I missed my period and spotted to where I had to wear a pantie liner for 3 days and it was brown...yikes, well my dad has mentioned that I am " getting fat " and he recently told me that I am getting fat still, I've gained up to 113.6 pounds, well I'm 17 years old and I've been having these cramps especially at night when I try to lay on my stomach like it is pulling up or something but it is on and off... does birth control do this ? I am on junel fe 1/20 and my lower back has been bugging me some too and I've been eating and peeing more than I should